1. Field of the Invention
The present invention relates to a single-ended swash plate compressor for use in automotive vehicle and like and in particular to a single-ended swash plate compressor which guides the piston at both the front a nd rear ends.
2. Description of the Related Art
Swash plate compressors, in which a plurality of cylinder bores are disposed parallel to a drive shaft in a peripheral portion of a cylinder block, with piston assemblies housed in the cylinder bores, the piston assemblies being caused to reciprocated by a swash plate which rotates together with the drive shaft, so as to compress a refrigerant gas, are in general use as compressors for conventional automotive air-conditioners. Moreover, double-ended swash plate compressors, which include double-headed piston assemblies in which compression pistons are formed on both ends of the piston rods and a compression action is performed at both the front end and the rear end of the piston bores, are often used. However, when using carbon dioxide (CO.sub.2) as a refrigerant in order to avoid using chlorofluorocarbons, there is a tendency to use single-ended swash plate compressors. In general, conventional single-ended swash plate compressors include single-headed piston assemblies in which compression pistons are formed on one end of the piston rods only and the compression action is performed at one end of the piston bores, for example, the rear end only, but recently methods have been developed to reduce misalignment of the axes between the piston assemblies and the cylinder bores in which guide pistons are formed at the other end of the piston rods and the piston assemblies are supported at both the front and rear ends, that is, by both the guide pistons and the compression pistons.
FIG. 4 is a partial cross-section of the vicinity of a cylinder bore in an example of a single-ended swash plate compressor in which the piston assemblies are supported at both the front and rear ends. In the figure, a cylinder assembly 51 is formed by joining a front cylinder block 51a and a rear cylinder block 51b. A swash plate chamber 52 is formed in the center of the cylinder assembly 51, and cylinder bores 61, 62 are formed in the front cylinder block 51a and the rear cylinder block 51b, respectively, around the swash plate chamber 52. The cylinder bores 61, 62 are formed in a plurality of pairs, each having the same diameter and being disposed equidistantly in a circle of prescribed radius around a drive shaft 63, and the cylinder bores 61 in the front cylinder block 51a each have the same center as the corresponding cylinder bores 62 in the rear cylinder block 51b. Housings are disposed at the end of the front cylinder block 51a and the end of the rear cylinder block 51b, respectively, and are fastened by bolts, but in this figure, only part of the housing 53 at the front end is shown.
Piston assemblies 55, which are housed in the cylinder bores 61, 62 comprise: guide pistons 55b, which are formed on the front end of piston rods 55a; and compression pistons 55c, which are formed on the rear end of the piston rods 55a. Each of the piston assemblies 55 has a swash plate engaging portion 55d in the center of the piston rod 55a, and a pair of shoe receivers 55e formed in the swash plate engaging portion 55d engage a pair of shoes 58, and thus engage a swash plate 57 by means of the shoes 58.
The front cylinder bores 61 normally connect to the inner chamber of the housing 53, which is connected to the intake side, and the rear cylinder bores 62 connect to the discharge side and the intake side through discharge valves and intake valves, which are not shown. The clearance between the guide pistons 55b and the front cylinder bores 61 (hereinafter called "side clearance") and the side clearance between the compression pistons 55c and the rear cylinder bores 62 are formed to the same dimensions.
The drive shaft 63 is supported rotatably by radial bearings 64, 65 in the center of the cylinder blocks 51a, 51b. A boss portion 57a is secured to the swash plate 57 in the center of the drive shaft 63. Thrust bearings 66, 67 are disposed between the boss portion 57a and the cylinder blocks 51a, 51b and support the load in the axial direction of the swash plate 57.
Consequently, in this single-ended swash plate compressor, when the drive shaft 63 is driven by an external power source, the swash plate 57 rotates and reciprocates, and the piston assemblies 55 are made to reciprocate within the cylinder bores 61, 62 by means of the shoes 58. At this time, the piston assemblies 55 are guided by the guide pistons 55b and the compression pistons 55c, and the compression pistons 55c compress the refrigerant gas inside the cylinder bores 62.
However, in the single-ended swash plate compressor employing this method of supporting the piston assemblies 55 at both the front and rear ends, it is difficult to avoid manufacturing problems, such as the cylinder bores 61, 62 being deformed by the fastening of the housings (53, etc.) to the cylinder blocks 51a, 51b by the bolts or by the pressure of the refrigerant gas charged in the compressor, or, as shown in FIG. 5 (in order to explain misalignment of the axes, the side clearance and misalignment of the axes in this figure are slightly exaggerated), the center lines 61A of the front cylinder bores 61 and the center lines 62A of the rear cylinder bores 61 being out of alignment with respect to the center lines 55A of the cylinders on the plans for the piston assembly 55. For that reason, when trying to reduce the side clearance which is formed between the pistons 55c and the cylinder bores 62 in order to reduce blowback and increase compression efficiency, there is a risk that partial interference will occur between the pistons 55b, 55c and the cylinder bores 61, 62 due to the kind of deformation and misalignment of the axes of the cylinder bores 61, 62 mentioned above, or that the work required to cause the pistons to reciprocate will increase, or that friction and abrasion will occur in the interfering portions.